Chapter 5: Under the Radar

After a brief conversation, one of the rebel men will lead you upstairs to a room with a hole in the floor. Drop down and you'll enter a small room with boarded-up windows. Blast away the boards and the zombies outside will smash in the glass, giving you an escape. Take out the zombies from inside the room (you can use the saw blades on the ground for free projectiles) before hopping out of the room and clearing the area. The zombies and headcrabs in the area are pretty tame, but watch for the radioactive goop on the ground around you.

When the enemies are cleared, hop onto a truck to the right so you can reach the upper level of a nearby building. Move the boards away using the Gravity Gun so you can move into the building and follow its halls to another outdoor area with yet more zombies. The zombies are more or less oblivious to your presence, though you may need to fend 'em off if you get close. Walk forward a bit and look to your right for a dip in the ground that goes under a pulled-up fence.

On the other side of the fence, far across the yard, is a mounted gun that's zapping everything it sees. Crawl under the fencing but stay ducked once you're on the other side. Lay low as you crawl toward the large pipe just ahead and watch for a burning headcrab that comes at you from the other side of the large pipe.

Crawl through the pipe and stay ducked down behind the row of cars that run in front of the deadly gun. As you move right, a small turret will begin firing at you from behind some boxes. Use the Gravity Gun to pick up a nearby barrel and toss it directly at the turret to knock it over, letting you proceed without hindrance. Eventually you'll reach the window of a building. Inside the building are a couple of Combine soldiers shooting you. Take 'em out, then hop in the building.